1. Field of the Invention
The present invention relates to a method for driving a plasma display panel.
2. Description of the Related Art
AC (alternating current) plasma display panels (to be referred to as PDP) are currently commercially available for use as thin display devices. A PDP houses two substrates consisting of a front transparent substrate and a rear substrate arranged in mutual opposition and separated by a predetermined gap. A plurality of row electrode pairs mutually forming pairs and respectively extending in the horizontal direction of the screen are formed on the inner surface of the front transparent substrate (surface opposing the rear substrate) serving as the display surface. Moreover, a dielectric layer covering each row electrode pair is formed on the inner surface of the front transparent substrate. A plurality of column electrodes extending in the vertical direction of the screen so as to intersect the row electrode pairs are formed on the rear substrate. When viewed from the display surface, display cells corresponding to pixels are formed at the intersections of the row electrode pairs and column electrodes.
Grayscale driving using a subfield method is carried out for this type of PDP so as to obtain half-tone display luminance corresponding to an input video signal.
In grayscale driving using a subfield method, display driving for one field's worth of a video signal is carried out for each of a plurality of subfields to which a number of times (or time period) light is to be emitted has respectively been assigned. In each subfield, an address step and a sustain step are carried out sequentially. In the address step, a selective discharge is selectively induced between the row electrodes and column electrodes in each display cell corresponding to an input video signal to form (or delete) a predetermined amount of wall charge. In the sustain step, only those display cells in which a predetermined amount of wall charge has been formed are made to discharge repeatedly to maintain a luminescent state accompanying that discharge. Moreover, a reset step is carried out prior to the address step in at least the first subfield. In this reset step, the amounts of wall charge remaining in all display cells are initialized by inducing a reset discharge between the pairs of row electrodes in all display cells.
Here, since the reset discharge is a comparatively strong discharge and is not involved in any manner with the contents of the image to be displayed, there was the problem of luminescence accompanying this discharge lowering image contrast.
Therefore, a PDP and driving method thereof have been proposed in which discharge delay time is attempted to be shortened by adhering magnesium oxide crystals, which exhibit cathode luminescence having a peak within a wavelength of 200 to 300 nm as a result of being excited by electron beam irradiation, to the surface of a dielectric layer covering row electrode pairs. For example, Japanese Patent Kokai No. 2006-54160 (Patent Document 1) discloses this PDP and its driving method. According to this PDP, since priming effects following discharge are made to persist for a comparatively long period of time, a weak discharge can be generated with stability. Therefore, by applying a reset pulse having a pulse waveform, in which the voltage value gradually reaches a peak voltage value with the passage of time, to the row electrodes of a PDP as described above, a weak reset discharge is made to occur between mutually adjacent row electrodes. In this process, since the emission luminance accompanying reset discharge decreases as a result of weakening this discharge, image contrast can be enhanced.
However, since it is not possible to adequately enhance so-called black contrast when displaying dark images even by using a driving method like that described above, there was the problem of being unable to provide dark images with high image quality.